1.Field of the Invention
The present invention relates to the production of electrical and electronic components, parts and the like of various types in which processing of structures in the micron range is necessary using an exposure process. In particular, the invention relates to electronic parts such as semiconductor devices, liquid crystal substrates, micromachines and the like, in which various electronic components and the like are formed on a workpiece using an exposure process in which light is emitted via a mask onto a workpiece on which a mask pattern is exposed. Still further, the invention relates to a contact exposure process in which the mask and the workpiece are located directly tightly adjacent to one another and the mask pattern is transferred to the workpiece which is thin and brittle, such as a printed board made of polyimide or the like (FPC).
2.Description of the Related Art
FIGS. 5(a) & 5(b) schematically show a known arrangement of a contact exposure device in which, by means of subatmospheric pressure, the space between the photomask (hereinafter called "mask M" ) and a workpiece W is subjected to a force with which the mask M and the workpiece W are pressed against one another and in which, thus, the mask and workpiece are arranged directly tightly adjacent to one another and exposure is performed. FIG. 5(a) is an plan view, while FIG. 5(b) is a cross-sectional view corresponding to line A-A in FIG. 5(a).
In the figures, a mask carrier MS is shown with positioning parts 1. Furthermore, the mask carrier MS is provided with an opening 2 so that exposure light is emitted from a light irradiation part (not shown) and directed via the mask M onto the workpiece W.
The mask M in which a mask pattern is formed is seated bordering the positioning parts 1 on the opening 2 with which the mask carrier MS is provided. The vicinity of the circular opening 2 of the mask carrier MS is provided with a suction groove 3. The mask M is attached and restrained on the mask carrier MS by a vacuum which is supplied to the suction groove 3 from a vacuum source (not shown). In the mask carrier MS, there is a passage 4 to reduce the pressure in the space, which is formed by the photomask M, the mask carrier MS, the workpiece W, a workpiece carrier WS and sealing parts 6 made of rubber of the like, to produce a vacuum state in order to hold the mask M and workpiece W directly tightly to one another.
The workpiece carrier WS is provided with a passages 5 for suctioning of the workpiece W to the workpiece carrier WS, so that the workpiece W seated on the workpiece carrier WS is retained on the workpiece carrier WS by a vacuum which is supplied to the passages 5 from a vacuum source (not shown), i.e., the workpiece carrier WS functions as a vacuum chuck.
The workpiece carrier WS is located via a device for adjusting the distance 7 on a workpiece carrier drive device 8 which moves the workpiece carrier WS in the X, Y & Z directions (see legends in FIGS. 5(a) and 5(b), for example), and furthermore, turns it around an axis perpendicular to the surface of the workpiece W, i.e., about the Z axis (hereafter, "movement in the .theta.-direction" ). The shape of the workpiece carrier WS is conventionally matched to the shape of the workpiece W. For example, the workpiece carrier WS is made circular when the workpiece is circular and rectangular when the workpiece W is rectangular, and with the opening 2 being similarly circularly or rectangularly shaped.
In the following, the known process for exposure of the workpiece W using the contact exposure device shown in FIG. 5(a) and 5(b) is described.
(1) The mask M is placed against the positioning parts 1 and seated on the mask carrier MS. Then, a vacuum is supplied to the suction groove 3, by which the mask M is retained on the mask carrier MS. PA0 (2) The workpiece W is seated on the workpiece carrier WS. A vacuum is supplied to the passage 5 from a vacuum source, by which the workpiece W is retained on the workpiece carrier WS. PA0 (3) The workpiece carrier WS is raised by means of the workpiece carrier drive device 8 into contact with the mask M. By means of device 7, the mask M and workpiece W are arranged parallel to one another (the manner in which the "parallel arrangement"0 of the mask M and the workpiece W relative to one another is produced can be found described, for example, in Japanese patent disclosure document HEI 7-74096 and corresponding, U.S. Pat. No. 5,543,890). PA0 (4) After arranging of the mask M and the workpiece W parallel to one another, the workpiece carrier WS is lowered slightly. The distance between the mask M and the workpiece W is set to the alignment distance. By means of an alignment microscope (not shown) the positions of alignment marks which are recorded on the mask M and the workpiece W are determined. The workpiece carrier WS is moved by means of the workpiece carrier drive device 8 in the X-Y-.theta.directions so as to bring the two alignment marks into agreement with one another. Thus, alignment of the mask M relative to the workpiece W is performed. PA0 (5) After completion of alignment, the workpiece carrier WS is raised and the mask M and the workpiece W are brought into contact with one another. In this case, solely by bringing the mask M and the workpiece W into contact with one another, the mask M and workpiece W cannot be arranged so that they are directly tightly adjacent to one another over all their entire surfaces if the mask M and/or the workpiece W have curvatures, microscopically small concave/convex points and the like. Between the mask M and the workpiece W, therefore, gaps arise in places, as is illustrated in FIG. 6 (in FIG. 6 they are shown exaggerated). If exposure is performed in this state, the exposure power (pattern shape after development) differs after exposure according to the exposed points. To arrange the mask M and the workpiece W over all the surfaces directly tightly adjacent to one another, therefore, the space between mask M and a workpiece W is subject to a force with which the two are pressed against one another, as described above. PA0 (6) The workpiece carrier WS is raised. The mask M and workpiece W are brought into contact with one another. In this way, the vacuum sealing parts 6, in the vicinity of the workpiece carrier WS, come into contact with the bottom of the mask carrier MS. A sealing space is formed by the mask M, the mask carrier MS, the workpiece W, the workpiece carrier WS and the vacuum sealing parts 6. In this state, a vacuum is supplied to the passage 4 located in the mask carrier MS, and thus, the pressure of the above described sealing space is reduced. PA0 (7) When the pressure of the sealing space is reduced, the mask M is pressed against the workpiece W so that the mask M and the workpiece W are arranged directly tightly against one another over their entire facing surfaces, as illustrated in FIG. 7. PA0 (8) In the above described state in which the mask M and the workpiece W are arranged directly tightly against one another, light which contains exposure light from a light irradiation part which (not shown) is emitted via the mask M onto the workpiece W, and thus exposure is performed.
As was described above, in the conventional contact exposure process, the pressure of the space between the mask M and the workpiece W is reduced, the mask M is subject to a force which deforms it in such a way that its shape is matched to the shape of the workpiece W, the workpiece W is clamped between the mask M and the workpiece carrier WS, and thus, the mask M and the workpiece W are arranged directly tightly against one another.
However, in this conventional process, the workpiece W is deformed when there is, for example, microscopically small dust on the workpiece carrier WS, as is illustrated in FIG. 8. When the mask M and the workpiece W tightly adjoin one another, therefore, the point on the mask M with which the deformed point on the workpiece W comes into contact is exposed to an intense force; this can lead to damaging-of the expensive-mask-M. If exposure is performed using a damaged mask, the damage is transferred in unchanged form to the workpiece W, yielding a faulty product.
Furthermore, the deformed point on the workpiece W is also exposed to an intense force, resulting in the danger of damage to the workpiece W. Especially recently, a workpiece W with a small thickness of roughly 50 to 100 microns has been used more and more often, such as a printed board (FPC) of polyimide or the like. On the other hand, there is a demand for higher image resolution, and accordingly, a tendency toward increasing the contact force between the mask M and the workpiece W. Therefore, there is greater and greater danger of damage to the workpiece W.